Oximeter sensor with digital memory recording sensor data

ABSTRACT

The present invention provides a memory chip for use in an oximeter sensor, or an associated adapter or connector circuit. The memory chip allows the storing of different data to provide enhanced capabilities for the oximeter sensor. In addition to providing unique data to store in such a memory, the invention describes unique uses of data stored in such a memory. The data stored in the memory chip may include information relating to use of the oximeter sensor. For example, the memory chip may encode a sensor model identification that can be displayed on a display screen when the sensor is connected to an oximeter monitor. The memory may also encode a range of operating parameters such as light levels over which the sensor can function or a maximum drive current. The operating parameters are read and interpreted by a controller circuit to control the pulse oximetry system.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/943,805 now U.S. Pat. 6,591,123, filed Aug. 30, 2001, whichclaims the benefit of U.S. Provisional Patent Application No.60/229,616, filed Aug. 31, 2000, which are hereby incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention relates to oximetry sensors and, in particular,pulse oximetry sensors which include coded information relating tocharacteristics of the sensor.

Pulse oximetry is typically used to measure various blood flowcharacteristics including, but not limited to, the blood-oxygensaturation of hemoglobin in arterial blood, the volume of individualblood pulsations supplying the tissue, and the rate of blood pulsationscorresponding to each heartbeat of a patient. Measurement of thesecharacteristics has been accomplished by use of a non-invasive sensorwhich passes light through a portion of the patient's tissue where bloodperfuses the tissue, and photoelectrically senses the absorption oflight in such tissue. The amount of light absorbed is then used tocalculate the amount of blood constituent being measured.

The light passed through the tissue is selected to be of one or morewavelengths that are absorbed by the blood in an amount representativeof the amount of the blood constituent present in the blood. The amountof transmitted light passed through the tissue will vary in accordancewith the changing amount of blood constituent in the tissue and therelated light absorption. For measuring blood oxygen level, such sensorshave been provided with light sources and photodetectors that areadapted to operate at two different wavelengths, in accordance withknown techniques for measuring blood oxygen saturation.

An encoding mechanism is shown in U.S. Pat. No. 4,700,708, thedisclosure of which is incorporated herein by reference. This mechanismrelates to an optical perfused tissue, with a detector picking up lightwhich has not been absorbed by the tissue. The operation depends uponknowing the wavelength of the LEDs. Since the wavelength of LEDs canvary, a coding resistor is placed in the probe with the value of theresistor corresponding to the actual wavelength of at least one of theLEDs. When the oximeter instrument is turned on, it first applies acurrent to the coding resistor and measures the voltage to determine thevalue of the resistor and thus the value of the wavelength of the LED inthe probe.

U.S. Pat. No. 5,259,381 recognizes that the coded value of thewavelength of the red LED provided by a coding resistor may beinaccurate, since the actual wavelength can vary with temperature.Accordingly, this patent teaches including a temperature sensor in theoximeter probe to measure the actual temperature. With the actualtemperature, and the coded wavelength value, a look-up table can beconsulted to determine the actual LED wavelength for that temperature.

Another method of storing coded information regarding thecharacteristics of the LEDs is shown in U.S. Pat. No. 4,942,877 assignedto Minolta. This patent discloses using an EPROM memory to store digitalinformation, which can be provided in parallel or serially from thesensor probe to the remote oximeter. The memory is described as storingcoefficients for the saturation equation, wavelength, subwavelength(where 2 peaks for LED), half-width of wavelength spectrum emitted byLED, intensity of LEDS or ratio, and on time of LEDS (written by theprocessor).

Other examples of coding probe characteristics exist in other areas.Multiple calibration values are sometimes required, with this making thecircuitry more complex or requiring many leads. In U.S. Pat. No.4,446,715, assigned to Camino Laboratories, Inc., a number of resistorsare used to provide coded information regarding the characteristics of apressure transducer. U.S. Pat. No. 3,790,910 discloses another pressuretransducer with a ROM storing characteristics of the individualtransducer. U.S. Pat. No. 4,303,984 shows another probe with digitalcharacterization information stored in a PROM, which is read seriallyusing a shift register.

Typically, the coding element is mounted in the probe itself. Forinstance, U.S. Pat. No. 4,621,643 shows the coding resistor mounted inthe probe element itself. In addition, U.S. Pat. No. 5,246,003 shows thecoding resistor being formed wmth a printed conductive material on theprobe itself.

In some devices, an electrical connector coupled by a cable to a deviceattached to a patient may include a coding element. For example, U.S.Pat. No. 3,720,199 shows an intra-aortic balloon catheter with aconnector between the catheter and a console. The connector includes aresistor with a value chosen to reflect the volumetric displacement ofthe particular balloon. U.S. Pat. No. 4,684,245 discloses a fiberopticcatheter with a module between the fiberoptic and electrical wiresconnected to a processor. The module converts the light signals intoelectrical signals, and includes a memory storing calibration signals sothe module and catheter can be disconnected from the processor and usedwith a different processor without requiring a recalibration.

U.S. Pat. No. 5,645,059 teaches using a modulated signal to provide thecoded data to a remote analyzer. U.S. Pat. No. 5,429,129 shows using avoltage regulator to produce a specific voltage value in response to anattempt to read by the analyzer.

Hewlett-Packard Company U.S. Pat. No. 5,058,588 teaches an oximetersensor with an encoding element that could be resistor, ROM, orcustomized integrated circuit. The encoding element encodes the type ofsensor (in particular, type indicating area of placement on body—finger,ear, foot, arm; also, the type of sensor can indicatetransmission/reflection type, or adult/neonate {indicating correction tobe performed on theoretical oxygen saturation, allow switching betweenphysiological limits such as minimum/maximum pulse rates foradults/neonates}; the maximum driving current may be adapted accordingto type of sensor, and contact of sensor with tissue can be tested bymeans of an attenuation measurement if sensor type is known).

Nellcor U.S. Pat. No. 5,645,059, the disclosure of which is herebyincorporated herein by reference, teaches coding information in sensormemory used to provide pulse modulated signal, to indicate the type ofsensor (finger, nose), the wavelength of a second LED, the number ofLEDs, the numerical correction terms to the standard curves, and anidentifier of the manufacturer.

A number of catheter patents also discuss encoding information in thecatheter. Sentron U.S. Pat. No. 4,858,615 teaches encoding the type ofsensor, type number, serial number, date of production, safe use life ofthe sensor, correction data for non-linearity, pressure sensitivity,offset, and temperature sensitivity.

Interflo Medical Published PCT Application No. PCT/US92/08263,Publication No. WO 93/06776 teaches encoding patient specific data,size, manufacture date, batch number, sterilization date, expirationdate, transducer number and type, manufacturer's name and address,thermistor heating element resistance, filament efficiency, programsegments or patient historical data., format version for the calibrationdata, trademark information, catheter unique serial number, ship date,other date and time information, security code to identify manufacturer,thermal mass, filament composition, coefficient of resistance, layoutbyte, checksum, copyright, number of seconds since a certain date,patient weight, patient height, timestamp of 1st CO data point, and acount of all CO data points in EEPROM.

Dulex-Ohmeda of Boulder, Colo. markets an oximeter sensor product thatencodes data into resistor values representing pointers to a lookuptable containing coefficients (as in U.S. Pat. No. 4,700,708) as well asindicating a range of LED drive current to use with the sensor. The LEDsare driven with a higher or lower drive currents depending upon thevalue of the resistor in a particular sensor.

Honeywell U.S. Pat. No. 4,303,984 (expires Dec. 12, 1999) describes amemory which stores characterization information, such as linearizationinformation for a pressure sensor. Alnor Instrument U.S. Pat. No.5,162,725 describes storing both calibration and ID information in asensor memory. Seimans U.S. Pat. No. 5,016,198 describes a coding memoryin a sensor with data for defining sensor's characteristic curve. McBeanU.S. Pat. No. 5,365,462 describes a date code in a sensor memory.Honeywell U.S. Pat. No. 4,734,873 describes a pressure sensor with aPROM storing coefficients for a polynomial. Robert Bosch U.S. Pat. No.4,845,649 describes a PROM in a sensor storing correcting data.

McBean U.S. Pat. No. 5,371,128 relates to EEPROM in sensor with sensortype code and calibration data. McBean U.S. Pat. No. 5,347,476 describesan accuracy code. Otax U.S. Pat. No. 5,528,519 shows a PROM in aconnector for oximeter.

Square D Company U.S. Pat. No. 5,070,732 shows calibration data in asensor memory. Baxter U.S. Pat. No. 5,720,293 talks about differentcalibration information for a catheter, including a security code(encryption is discussed), serial number, model number, ID data such ascalibration, manufacture, sterilization and ship date or other date andtime information, a software program segment, security code foridentifying whether sensor made by same manufacturer as monitormanufacturer, filament or transducer resistance, heat transfercoefficient, thermal mass, filament composition and coefficient ofresistance, layout byte, copyright notice, checksum, random data bytes.Porsche U.S. Pat. No. 5,008,843 describes a sensor with EEPROM ID andcharacteristics data.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a memory chip for use in an oximetersensor, or an associated adapter or connector circuit. The memory chipallows the storing of different data to provide enhanced capabilitiesfor the oximeter sensor. In addition to providing unique data to storein such a memory, the invention describes unique uses of data stored insuch a memory. The data stored in the memory chip includes informationrelating to use of the oximeter sensor. For example, the memory chip mayencode a sensor model identification that can be displayed on a displayscreen when the sensor is connected to an oximeter monitor. The memorymay also encode a range of operating parameters such as light levelsover which the sensor can function or a maximum drive current. Theoperating parameters are read by a controller circuit which uses thedata read from the memory chip to control the functioning of the pulseoximetry system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a pulse oximeter system in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of a pulse oximeter system incorporating acalibration memory element 56 according to the invention. In oneembodiment, memory element 56 is a two-lead semiconductor digital memorychip. The calibration element is part of the sensor 50 which alsoincludes red and infrared LEDs 52 as in the prior art, along with adetector 54. If desired, LEDs 52 may be replaced with other lightemitting elements such as lasers.

The oximeter includes read circuit 60, drive circuit 66, look-up tables62 and 63, controller 64, amplifier 72, filter 74, and analog-to-digitalconverter 76. Read circuit 60 is provided for reading multiple codedvalues across the two leads 51, 53 connected to calibration element 56.One value is provided to a look-up table 62 to determine appropriatewavelength dependent coefficients for the oxygen saturation calculation,as in the prior art. The other value(s) are then provided to anotherlook up table(s) 63 which provides input (e.g., coefficients) to othercalculations performed by controller 64. These additional calculationsmay enhance the performance and/or safety of the system. Controller 64provides signals to a drive circuit 66, to control the amount of drivecurrent provided to LEDs 52.

As in the prior art, detector 54 is connected through an amplifier 72and a filter 74 to an A/D converter 76. This forms a feedback path usedby controller 64 to adjust the drive current to optimize the intensityrange of the signal received. For proper operation the signal must bewithin the analog range of the circuits employed. The signal should alsobe well within the range of A/D converter 76 (e.g., one rule that may beapplied is to adjust LED drives and amplifier gains so that both red andIR signals fall between 40% and 80% of full scale reading of converter76). This requires correct and independent settings for both the red andinfrared LEDs. The current invention allows for another feedback pathwhich may alter the LED settings based on other sensor characteristicscontained in the coding of the calibration element 56, which isdiscussed in further detail below.

Memory 56 may, for example, be implemented as a random access memory(RAM), a FLASH memory, a programmable read only memory (PROM), anelectrically erasable PROM, a similar programmable and/or erasablememory, any kind of erasable memory, a write once memory, or othermemory technologies capable of write operations. Various types of datauseful to a pulse oximetry system can be stored in memory 56. Forexample, data indicating a sensor model identification codecorresponding to a particular sensor model can be encoded in memory 56.Also, an action can be encoded into memory element 56 indicating anaction to be performing by the oximeter monitor in response to readingthe sensor model identification code.

For example, an identification code in the form of text indicating thespecific model of sensor can be digitally encoded into memory 56 andread by the oximeter monitor when the sensor is connected to theoximeter. An action indicating that the sensor model text is to bedisplayed by the oximeter monitor on a display screen can also beencoded in memory 56. The identification code can be displayed in humanreadable form on a display screen connected to the pulse oximetermonitor. The identification code allows the oximeter instrument todisplay a text string indicating what sensor model is being used, e.g.“Nellcor OXISENSOR II D-25,” “Adult Digit Sensor,” or “Agilent N-25.”

Alternately, display text for a plurality of specific models of pulseoximeter sensors can be stored in a lookup table coupled in parallelwith lookup tables 62 and 63 in the pulse oximeter monitor. The pulseoximeter monitor reads a sensor code from memory 56 when the sensor 50is connected to the oximeter. The sensor identification code stored inmemory 56 is used to locate display text stored in a lookup table thatcorresponds to a specific sensor model. The oximeter can display thedisplay text for the specific sensor model on a display screen forviewing.

The present invention eliminates the need for printing a model name andnumber on the sensor itself. Even when model names and numbers areprinted on a sensor, the text may become illegible after several uses.Displaying text that corresponds to a specific sensor model can behighly useful for users of pulse oximetry sensors. For example, it maybe important to identify a sensor model so that instructions relating toa particular sensor model in the manufacturer's handbook can beidentified. In addition, it may be necessavy to identify a sensor modelname or identification number when corresponding with the manufacturer.

Digitally encoded data indicating a sensor model type in memory 56 or ina lookup table may be used to determine whether a sensor model iscompatible with a particular pulse oximeter monitor. For example, memory56 may contain a code indicating a sensor model type that is read bycontroller 64. Memory 56 can also encode an action indicating thatcontroller 64 is to compare the code from memory 56 with a list of codesin a lookup table (or other oximeter monitor memory device) to determineif the sensor is compatible. If controller 64 successfully matches thecode read from the sensor, the display text indicating the sensor modeltype is displayed on the display screen. If controller 64 does notrecognize the code, an error message may be displayed on the displayscreen indicating that the oximeter monitor does not recognize thesensor, and the oximeter may refuse to operate until the sensor isreplaced.

A code can be stored in the sensor memory 56 identifying the sensormanufacturer. An action indicating a use for the code by the oximetercan also be stored in memory 56. The code is read by controller 64 andis used for the purpose indicated by the action. The action may, forexample, indicate that the code in memory 56 is to be used to indicateoperability with oximeter monitors of other manufacturers. Controller 64can recognize certain codes as indicating compatible oximeter sensors.If the oximeter monitor does not recognize the code, then controller 64can display an error message on a display screen indicating that thesensor is not compatible, and/or controller 64 can shut down circuitryin the oximeter monitor that senses signals from the sensor until thesensor is replaced with a compatible sensor.

Other information may also be encoded into memory 56, read by theoximeter monitor and displayed for user reference. For example, languagecodes or country codes can be stored in memory 56, read, and displayedto the user. The user can select a language or country code so thatmessages are displayed such as error messages are displayed in theselected language or a language corresponding to the selected country.Messages may also be encoded into memory 56. For example, safetymessages relating to the proper use of the sensor can be encoded inmemory 56 and displayed on a display screen in human-readable form.

It is often desirable to upgrade the algorithms that are used by theoximeter to determine blood oxygen saturation levels, pulse rates, pulseamplitude, blood pressure, and other patient data as technologyprogresses and the operating parameters (such as filter coefficients)are refined. Because oximeter sensors are typically much less expensiveto replace than oximeter monitor instruments, it is desirable to encodedata corresponding to the updated algorithms in the sensors rather thanin the oximeter monitors.

One method for performing these updates is by encoding revisions to thealgorithms used for calculating the patient parameters in memory withinthe oximeter monitor, while encoding updated software code or tuningcoefficients in sensor memory 56. The updated code or coefficientscorrespond to updated algorithms that are read by the oximeter monitorso that the updated algorithms can be applied to the standard algorithmspreprogrammed into the oximeter. For example, a line of software code inan algorithm used by the oximeter monitor can be replaced by a updatedline of code stored in memory 56.

Controller 64 can read the updated code or coefficients from memory 56and apply the updated algorithms to signals received from detector 54 todetermine accurate blood oxygen saturation levels, pulse rates, pulseamplitudes, perfusion data, blood pressure, and other patient data. Theupdated algorithms can also be used to allow only supported features tobe used. In the preferred embodiment, once updated, the new code orcoefficients become permanently stored in the oximeter monitor, alongwith a new algorithm revision number, and are utilized for all futuresensor use until later updated.

Encoding a sensor model identification code could also be used toaccommodate sensor-specific operating parameters such as LED drivecurrents or “sensor off” characteristics (as an alternative toprogramming the value of drive current or “off” characteristicsthemselves). Under normal operating conditions, photosignals coming fromthe sensor LEDs generally fall within a certain range. When a sensor isremoved from a patient, or falls off on it's own, the photosignalusually changes. This is particularly true for the reusable clip-stylesensor, because in their normal disconnected state, the LEDs shinedirectly onto the photodetector unimpeded by, for example, tissue! Byprogramming a “threshold photocurrent” into memory chip 56, reliabledetection of a “sensor is off the patient” condition can beaccomplished. In this example, exceeding a certain detected thresholdlight level is a sure sign the sensor isn't on a finger or other opposedsite.

For certain other sensors, a low light level may be indicative of thesensor being off. An adhesive sensor, for example, lays flat when init's natural state—little LED light may reach the detector. Encoding anexpected range of light levels for the specific model of sensor beingused into memory 56 allows enhanced detection of when the sensor isimproperly placed or has been removed. When controller 64 senses thatthe light level output detector by photodetector 54 has fallen below orexceeded the expected range of light levels encoded into memory 56, theoximeter monitor can display an “sensor off” message on a display screenindicating to the medical personnel that the sensor is not in anoperable position and that valid data cannot be detected (i.e., a sensoroff condition). The oximeter monitor can also emit an alarm signal untilthe light level detected by photodetector 54 reaches the expected range.

If desired, expected ranges of light levels (or other parameters such aspulse size) that are specific to a particular patient may be encoded andsaved into memory 56 by the clinical through the oximeter. The oximetercompares the expected range for the parameters encoded into memory 56with data received from the photodetector to determine a sensor offcondition each time the sensor is used until the range data isoverwritten with new data. This is advantageous because light levels,pulse sizes, and other parameters detected by the photodetector can varysignificantly from patient to patient.

Existing pulse oximeter sensors determine whether a sensor is off thepatient, or not in good contact, by using a number of metrics. Thosemetrics include pulse size, pulse variability, IR/Red correlation, lightlevel variability, pulse shape, and pulse regularity. Not only the lightlevel, but any of these other values could vary depending on the type ofsensor, the characteristics of an individual patient, and the locationon the body where the sensor is to be applied. Thus, sensor memory 56could encode information about the expected variation in any of thesemetrics for the particular sensor type or model or a particular patient,for use in determining if a sensor is off from any combination of theseor other metrics as an indication that the sensor is off the patient.

For example, pulses could be typically weaker on the forehead comparedto the finger. Memory device 56 of an oximeter sensor designed for useon the forehead of a patient can be encoded with a range of pulse sizesas well as a range of light levels that are expected from thatparticular oximeter sensor model. If desired, memory 56 can encode arange of numbers based upon light level and pulse size (and otherparameters). For example, memory 56 can encode a range of numbersrepresenting the expected range of pulse size times light level receivedfrom detector 54 for a specific sensor model.

Controller 64 reads and decodes the pulse size, light level range, andother data encoded in memory 56. Controller 64 then compares theexpected pulse size and light level range data with the informationreceived from detector 54. When the pulse size and/or light level datareceived from detector 54 exceeds or falls below the expected range dataencoded in memory 56, the oximeter monitor displays an output message,e.g., a warning of a poor signal, on the display screen indicating thatthe sensor is not operable or emits an alarm signal. Further details ofa Method and Circuit for Indicating Quality and Accuracy ofPhysiological Measurements are discussed in U.S. patent application Ser.No. 09/545,170, filed Apr. 6, 2000 to Porges, et al., which isincorporated by reference herein in its entirety.

Running LEDs 52 at a high drive current results in more light outputfrom the LEDs, thus improving the signal-to-noise ratio of the bloodoxygen saturation signal from detector 54, but comes at a cost ofcausing additional heat dissipation (i.e., the LEDs run “hotter”). Ascurrent flows through the sensor LEDs, the LED emits heat (i.e., the LEDpower=LED drive current times the voltage drop across the LED). Themajority of the energy output by the LEDs is dissipated as heat, and thesmaller portion of the energy output by the LEDs is emitted as light.This heat typically causes the temperature of the skin under the sensorto rise by an amount that that depends on the heat dissipationproperties of the sensor. Current safety regulations and guidelineslimit the temperature of the skin contacting portions of the sensor toremain at or below 41° C. Sensors that do a poor job of directing theheat away from the skin contacting surface, should use a lower LED drivecurrent. Sensors with good thermal management can utilize higher drivecurrents without risk to the patient.

Accordingly, by encoding the maximum safe LED drive current into thesensor itself, the oximeter instrument can utilize the highest safedrive current for the sensor being used to attain the greatest amount ofLED light without risk of injury. The maximum safe drive current allowedto achieve a skin temperature at or below a maximum level can bedetermined in advance through testing for a given oximeter sensor model.That maximum drive current can be encoded into memory 56 and read bycontroller 64 when the sensor is connected to the oximeter monitor.Controller 64 then communicates with drive circuit 66 to drive LEDs 52at or near the maximum drive current value read from memory 56, but toprevent circuit 66 from driving LEDs 52 with a current that exceeds themaximum drive current.

While the present invention has been described herein with reference toparticular embodiments thereof, a latitude of modification, variouschanges and substitutions are intended in the foregoing disclosure, andit will be appreciated that in some instances some features of theinvention will be employed without a corresponding use of other featureswithout departing from the scope of the invention as set forth.Therefore, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope and spirit of the present invention.It is intended that the invention not be limited to the particularembodiments disclosed, but that the invention will include allembodiments and equivalents falling within the scope of the claims.

1. An oximeter system comprising: a sensor comprising a light emittingelement; a light detecting element; and a data encoding means forstoring data, said data comprising a maximum safe drive current that canbe applied to said light emitting element; and an oximeter having acontroller configured to read the maximum safe drive current from thedata encoding means, and a drive circuit configured to drive the lightemitting element to the maximum safe drive current.
 2. The oximetersystem of claim 1 wherein said maximum safe drive current corresponds toa skin temperature at or below a maximum level.
 3. An oximeter systemcomprising: a sensor comprising a light emitting element; a lightdetecting element; and a data encoding means for storing digital data,said digital data comprising updated software code for use by anoximeter coupled to said sensor to calculate data encoded in signalsreceived from said light detecting element; and the oximeter having acontroller configured to read the updated software code from the dataencoding means and to apply the updated software code to calculationsperformed using the signals received from the light detecting element.4. An oximeter system comprising: a sensor comprising a light emittingelement; a light detecting element; and a data encoding means forstoring digital data, said digital data comprising a displayable messageand codes that correspond to a plurality of languages; and an oximeterconfigured to read the displayable message and the codes from the dataencoding means and to display the displayable message in a selectedlanguage.
 5. An oximeter system comprising: a sensor comprising a lightemitting element; a light detecting element; and a data encoding meansfor storing digital data, said digital data comprising a displayablemessage and codes that correspond to a plurality of countries that areselectable; and an oximeter configured to read the displayable messageand the codes from the data encoding means and to display thedisplayable message in a language corresponding to a selected country.6. A method for storing data in an oximeter sensor, the methodcomprising: emitting light from a light emitting element; detectinglight from the light emitting element using a photodetector; and storingdigitally encoded data in a memory in the sensor, the digitally encodeddata comprising a maximum safe drive current that can be applied to saidlight emitting element in said memory.
 7. The method of claim 6 furthercomprising: driving said light emitting element to said maximum safedrive current.
 8. A method for operating an oximeter system thatincludes a sensor and an oximeter monitor, the method comprising:emitting light from a light emitting element; detecting light from thelight emitting element using a photodetector; and storing digitallyencoded data in a memory in the sensor, the digitally encoded datacomprising updated software code for use by the oximeter monitor coupledto said oximeter sensor to calculate data from signals received fromsaid photodetector.
 9. The method of claim 8 further comprising:replacing a line of software code in an algorithm used by the oximetermonitor with the updated software code stored in the memory.
 10. Amethod for forming an oximeter sensor, the method comprising: providinga light emitting element in the oximeter sensor; providing a lightdetecting element in the oximeter sensor; and storing data in a dataencoding means in the sensor, the data comprising a maximum safe drivecurrent that can be applied to said light emitting element.
 11. Themethod of claim 10 wherein the maximum safe drive current corresponds toa skin temperature at or below a maximum level.
 12. A method for formingan oximeter sensor, the method comprising: providing a light emittingelement in the oximeter sensor; providing a light detecting element inthe oximeter sensor; and storing data in a data encoding means in theoximeter sensor, the data comprising a message and codes that correspondto a plurality of languages, wherein the message is displayable in aselected language.